Methods of Making Orthodontic Appliances

ABSTRACT

Methods of making a removable dental positioning appliance include forming a sheet of transparent crystalline polymeric material into a shell having cavities shaped to receive and reposition teeth from a first orientation to a successive orientation. The polymeric material may then be annealed at a temperature above its glass transition temperature or cured if a curable material to enhance characteristics of the polymeric material. The polymeric material may be coated with a second transparent material.

FIELD OF THE INVENTION

The present invention relates generally to orthodontics and, moreparticularly, to orthodontic appliances for incrementally moving teethfrom an initial tooth arrangement to a final tooth arrangement.

BACKGROUND OF THE INVENTION

Orthodontic treatments involve repositioning misaligned teeth andimproving bite configurations for improved cosmetic appearance anddental function. Repositioning teeth is accomplished by applyingcontrolled forces to the teeth over an extended period of time. This isconventionally accomplished by wearing what are commonly referred to as“braces.” Braces include a variety of appliances such as brackets,bands, archwires, ligatures, and O-rings. After braces are bonded to theteeth, periodic meetings with an orthodontist are typically required toadjust the braces. This may involve installing different archwires withdifferent force-inducing properties and/or may include replacing ortightening existing ligatures. Between meetings, the patient may berequired to wear supplementary appliances, such as elastic bands orheadgear, to supply additional or extraoral forces.

Although conventional braces can be effective, their use often is atedious and time consuming process that requires many visits to anorthodontist. Moreover, from a patient's perspective, braces areunsightly and uncomfortable. Consequently, alternative orthodontictreatments have developed. A particularly promising approach relies onthe use of elastic positioning appliances for realigning teeth. Suchappliances comprise a thin shell of elastic material that generallyconforms to a patient's teeth, but that is slightly out of alignmentwith the patient's initial tooth configuration. Placement of the elasticpositioner over the teeth applies controlled forces in specificlocations to gradually move the teeth into the new configuration.Repetition of this process with successive appliances having differentconfigurations eventually moves a patient's teeth through a series ofintermediate configurations to a final desired configuration. A fulldescription of exemplary elastic polymeric positioning appliances andmethods of using same are described in U.S. Pat. No. 5,975,893, commonlyassigned to the assignee of the instant invention and which isincorporated herein by reference in its entirety.

Polymeric positioning appliances, such as those described in the '893patent, are advantageous over conventional braces in that they are easyto use and they are generally transparent, providing an improvedcosmetic appearance. Unfortunately, polymeric materials currentlyutilized in the production of these positioning appliances may undergostress relaxation and creep, which can seriously degrade the ability ofan appliance to reposition teeth as desired. In addition, polymericmaterials currently utilized may be susceptible to degradation as aresult of exposure to saliva and other chemicals present within apatient's mouth.

SUMMARY OF THE INVENTION

According to embodiments of the present invention, a method of making aremovable dental positioning appliance includes forming a sheet oftransparent crystalline polymeric material into a shell having cavitiesshaped to receive and reposition teeth from a first orientation to asuccessive orientation and then annealing the shell at a temperatureabove the glass transition temperature of the transparent crystallinepolymeric material. Annealing is performed at a temperature and timesufficient to cause the annealed transparent crystalline polymericmaterial to preferably have a tensile strength at yield of greater than6,000 psi, preferably have an elongation at yield of greater than 4%,preferably have an elongation at break of greater than 80%, preferablyhave a tensile modulus greater than 200,000 psi, preferably have aflexural modulus greater than 200,000 psi, preferably have stressrelaxation over time of not more than 50%, and preferably have atransmissivity of light between 400 nm and 800 nm greater than 75%.

According to embodiments of the present invention, a method of making aremovable dental positioning appliance includes forming a sheet oftransparent curable polymeric material into a shell having cavitiesshaped to receive and reposition teeth from a first orientation to asuccessive orientation and then curing the polymeric material. Whencured, the transparent polymeric material preferably has a tensilestrength at yield of greater than 6,000 psi, preferably has anelongation at yield of greater than 4%, preferably has an elongation atbreak of greater than 80%, preferably has a tensile modulus greater than200,000 psi, preferably has a flexural modulus greater than 200,000 psi,preferably has stress relaxation over time of not more than 50%, andpreferably has a transmissivity of light between 400 nm and 800 nmgreater than 75%. Even more preferably, the cured transparent polymericmaterial has a tensile strength at yield of greater than 8,800 psi,preferably has an elongation at yield of greater than 5%, preferably hasan elongation at break of greater than 100%, preferably has a tensilemodulus greater than 300,000 psi, preferably has a flexural modulusgreater than 330,000 psi, preferably has stress relaxation over time ofnot more than 30%, and preferably has a transmissivity of light between400 nm and 800 nm greater than 80%.

According to embodiments of the present invention, a method of making aremovable dental positioning appliance includes forming a sheet oftransparent curable polymeric material into a shell having cavitiesshaped to receive and reposition teeth from a first orientation to asuccessive orientation and then coating the polymeric shell with asecond transparent material. If the coating is a curable material, theshell and coating are then subjected to curing operations to cure thecoating material. The coated appliance preferably has a tensile strengthat yield of greater than 6,000 psi, preferably has an elongation atyield of greater than 4%, preferably has an elongation at break ofgreater than 80%, preferably has a tensile modulus greater than 200,000psi, preferably has a flexural modulus greater than 200,000 psi,preferably has stress relaxation over time of not more than 50%, andpreferably has a transmissivity of light between 400 nm and 800 nmgreater than 75%. Even more preferably, the coated appliance has atensile strength at yield of greater than 8,800 psi, preferably has anelongation at yield of greater than 5%, preferably has an elongation atbreak of greater than 100%, preferably has a tensile modulus greaterthan 300,000 psi, preferably has a flexural modulus greater than 330,000psi, preferably has stress relaxation over time of not more than 30%,and preferably has a transmissivity of light between 400 nm and 800 nmgreater than 80%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a removable dental positioning appliancethat may be formed by various methods in accordance with embodiments ofthe present invention.

FIGS. 2-4 are flow charts illustrating methods of making a removabledental positioning appliance according to embodiments of the presentinvention

DETAILED DESCRIPTION OF THE INVENTION

The present invention now is described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. The terminology used in thedescription of the invention herein is for the purpose of describingparticular embodiments only and is not intended to be limiting of theinvention. As used in the description of the invention and the appendedclaims, the singular forms “a”, “an” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items.

U.S. Pat. No. 5,975,893 describes methods and systems for repositioninga patient's teeth from an initial tooth arrangement to a final tootharrangement by placing a series of polymeric shell appliances in thepatient's mouth. The appliances are not affixed to the patient's teethand the patient may place and replace the appliances at any time duringthe procedure. The first appliance of the series has a geometry selectedto reposition the teeth from the initial tooth arrangement to a firstintermediate arrangement. After the first intermediate arrangement isapproached or achieved, one or more additional (intermediate) appliancesare successively placed on the teeth, where such additional applianceshave geometries selected to progressively reposition teeth from thefirst intermediate arrangement through successive intermediatearrangement(s). The treatment is finished by placing a final appliancein the patient's mouth, where the final appliance has a geometryselected to progressively reposition teeth from the last intermediatearrangement to the final tooth arrangement. FIG. 1 illustrates anexemplary dental positioning appliance 10 described in the '893 patent.

The polymeric shells of dental positioning appliances for a patient,such as illustrated in FIG. 1, are produced by initially obtaining adigital data set (IDDS) representing an initial tooth arrangement. TheIDDS may be obtained in a variety of ways. For example, the patient'steeth may be scanned or imaged using well known technology, such asX-rays, three-dimensional x-rays, computer-aided tomographic images ordata sets, magnetic resonance images, etc. The IDDS is then digitallymanipulated via a computer to produce a final tooth arrangement, whichis incorporated into a final digital data set (FDDS). Based on both theIDDS and the FDDS, a plurality of intermediate digital data sets(INTDDS's) are generated to correspond to successive intermediate tootharrangements that correspond to tooth movement from the initial tootharrangement to the final tooth arrangement.

Using the intermediate and final data sets, positive tooth models of apatient's teeth corresponding to each of the intermediate and final datasets are produced. After the positive models are prepared, aconventional pressure or vacuum molding machine may be used to producethe polymer shells of dental positioning appliances from athermoformable material. The molding machine produces each of theappliances directly from a positive tooth model. The appliances aremarked in some manner, typically by sequential numbering directly on theappliances or on tags, pouches, or other items which are affixed to orwhich enclose each appliance, to indicate their order of use.

According to embodiments of the present invention, methods of makingremovable dental positioning appliances, such as illustrated in FIG. 1,with improved material properties are provided. Referring initially toFIG. 2, a method of making a removable dental positioning applianceaccording to an embodiment of the present invention includes forming asheet of transparent crystalline polymeric material into a shell havingcavities shaped to receive and reposition teeth from a first orientationto a successive orientation (Block 100) and then annealing the shell ata temperature above the glass transition temperature of the transparentcrystalline polymeric material (Block 110). Annealing is performed at atemperature and time sufficient to cause the annealed transparentcrystalline polymeric material to preferably have a tensile strength atyield of greater than 6,000 psi, preferably have an elongation at yieldof greater than 4%, preferably have an elongation at break of greaterthan 80%, preferably have a tensile modulus greater than 200,000 psi,preferably have a flexural modulus greater than 200,000 psi, preferablyhave stress relaxation over time of not more than 50%, and preferablyhave a transmissivity of light between 400 nm and 800 nm greater than75%.

Even more preferably, annealing is performed at a temperature and timesufficient to cause the annealed transparent crystalline polymericmaterial to preferably have a tensile strength at yield of greater than8,800 psi, preferably have an elongation at yield of greater than 5%,preferably have an elongation at break of greater than 100%, preferablyhave a tensile modulus greater than 300,000 psi, preferably have aflexural modulus greater than 330,000 psi, preferably have stressrelaxation over time of not more than 30%, and preferably have atransmissivity of light between 400 nm and 800 nm greater than 80%.

Preferably, the annealing temperature is between the glass transitiontemperature and melting temperature of the transparent crystallinepolymeric material (i.e., T_(g)<T_(anneal)<T_(m)). However, variousannealing temperatures may be utilized. Annealing is preferablyperformed for at least about one minute. However, annealing may beperformed for various time periods in accordance with embodiments of thepresent invention. Annealing times and temperatures will vary dependingon the material of the shell and the coating material, as would beunderstood by those skilled in the art.

According to embodiments of the present invention, annealing may beperformed in the presence of a nucleating agent disposed on or withinthe transparent crystalline polymeric material. As known to thoseskilled in the art, nucleating agents are chemical substances which,when incorporated in polymer materials, form nuclei for the growth ofcrystals in the polymer melt. For example, in certain polymers, a higherdegree of crystallinity and more uniform crystalline structure may beobtained by adding a nucleating agent.

According to embodiments of the present invention, annealing may beperformed selectively. The term “selective annealing” is used herein toindicate that a physical property of the transparent crystallinepolymeric material can be accurately controlled and modified to specificparameters via annealing. Selective annealing can allow forcustomization of a removable dental appliance. For example,crystallinity can be selectively increased, which can decrease theoptical transparency, in portions of the shell of a removable dentalappliance that are not visible when worn by a user. Other, visibleportions may have less crystallinity and, thereby, more transparency.Selective annealing can occur by heating only certain portions of theshell. Other properties of the transparent crystalline polymericmaterial which may be controlled via selective annealing include, butare not limited to, tensile strength at yield, elongation at yield,elongation at break, tensile modulus, flexural modulus, stressrelaxation, etc.

Annealing polymeric materials can also lead to densification of theamorphous phase, which is often referred to as physical aging. Suchdensification of amorphous phases can lead to an increase in modulus ofthe device.

Annealing may be performed by only heating selected portions of theshell of a removable dental positioning appliance. For example, a lightsource or laser may be utilized to heat selected portions of the shellof a removable dental positioning appliance. According to otherembodiments of the present invention, annealing may be performed byadding chemical crosslink agents only to certain areas of thetransparent crystalline polymeric material of the shell of a removabledental positioning appliance.

According to other embodiments of the present invention, annealing maybe performed by selectively subjecting the transparent crystallinepolymeric material to irradiation, such as e-beam irradiation,UV-visible irradiation and/or gamma irradiation.

According to embodiments of the present invention, exemplary transparentcrystalline polymeric materials include, but are not limited to, liquidcrystalline polymeric materials, styrenics, and ion-containing polymers.Applicants have discovered that removable dental positioning appliancesformed from liquid crystalline polymers, styrenics, and ion-containingpolymers that are annealed to have one or more of the above-listedcharacteristics are less susceptible to stress relaxation and creep thanconventional dental positioning appliances. Moreover, Applicants havediscovered that removable dental positioning appliances formed fromliquid crystalline polymers, styrenics, and ion-containing polymers thatare annealed to have one or more of the above-listed characteristics areless susceptible to degradation caused by exposure to saliva and otherchemicals in a patient's mouth. Annealing significantly reduces internalstress levels, which increases chemical resistance of the material.

Exemplary liquid crystalline polymeric materials according toembodiments of the present invention include, but are not limited tobranched liquid crystalline polymers and polyarylates. Crystallizablepolyester compositions are also suitable and are described in U.S. Pat.No. 5,405,921, which is incorporated herein by reference in itsentirety. Crystallizable polyesters utilized in accordance withembodiments of the present invention preferably have a glass transitiontemperature of at least 50° C. and/or a melting point of at least 150°C. In terms of intrinsic viscosity (IV), crystallizable polyestersshould have an IV of at least about 0.5 as measured in a 1:1 by weightsolution of methylene chloride and trifluoroacetic acid. The polyesterbase resin preferably is present in an amount of about 79-99 wt % basedupon the total weight of the formulations used in the practice of thisinvention. A single polyester material need not be used. Copolyestersand blends may be used.

To obtain a clear product based upon crystallized polyester, the polymermust be oriented prior to the onset of crystallization. The orientationof the polyester results in the formation of elongated crystallites.Elongated crystallites allow incident light to pass without substantialdiffraction, which results in a clear, transparent product.

Other exemplary crystalline polymeric materials that may be utilized inaccordance with embodiments of the present invention includepolyethylene terephthalate (PET) (e.g., DuPont Teijin Films Melinex® andpolyethylene naphthalate (PEN) films (e.g., DuPont Teijin Films Teonex®.PET and PEN films have an inherent advantage over amorphous polymerfilms because PET and PEN are both semi-crystalline and biaxiallyoriented polymers. Moreover, PET and PEN films will typically absorbapproximately 1,400 ppm of moisture at equilibrium.

According to other embodiments of the present invention, dentalpositioning appliances may be formed from PVC modified with Elvaloy®ketone ethylene ester (DuPont, Wilmington, Del.). Elvaloy® modified PVChas been found to be more resistant to creep than PVC and HDPE.

Exemplary styrenic polymeric materials according to embodiments of thepresent invention include, but are not limited to polystyrene (PS),expanded polystyrene (EPS), acrylonitrile-butadiene-styrene (ABS),styrene-acrylonitrile (SAN), styrene block copolymers (SBC), unsaturatedpolyester resins (uPES), styrene butadiene rubber (SBR), and styrenebutadiene latex (SBL). Styrenic polymeric materials are rigid,transparent, tough, resistant to grease, stress cracking and crazing.Styrenic polymeric materials are also easily processed and resistant tofood stains. Styrenic polymeric materials are available from a varietyof sources including Bayer AG, Leverkusen, Germany, The Dow ChemicalCompany, Midland, Mich., and PolyOne Corporation, Avon Lake, Ohio.

Exemplary ion-containing polymeric materials include, but are notlimited to, Surlyn® brand resin (DuPont, Inc., Wilmington, Del.). Otherimportant commercial ionomers include Nafion® brand polymers (Ion Power,Inc., Bear, Del.). Nafion® brand polymers are sulfonatedtetrafluorethylene ionomer and sulfonated polystyrene. Ionomers havesignificantly better properties than the un-ionized precursor becausethe ionic groups phase separate into ion-rich domains.

Other exemplary polymeric materials that can be formed and annealed, inaccordance with embodiments of the present invention, includetransparent polymeric materials with high glass transition temperatures(e.g., at least 155° C.). Exemplary transparent polymeric materialshaving high glass transition temperatures include, but are not limitedto norbornene-containing polymers, metallocene, metal-catalyzedpolyolefins, cyclo-olefins, poly(methyl-1-pentene), amorphous aromaticresins, poly(benzophenone)s, polyamides, thermoplastic polyurethanes,polyetherimides, poly(arylene ether ketone)s, polysulfones, biphenylendcapped poly(acrylene ether) polymers, polycarbonates, polyesters,poly(estercarbonate)s, cellulosics, and acrylics.

Other exemplary transparent materials having high glass transitiontemperatures include Paramax® (Mississippi Polymer Technologies) andpolyamides. Paramax® is a very hard polymer with a low coefficient ofthermal expansion, and a high refractive index. Paramax® can be moldedextruded and cast from solution and produces clear alloys with otherengineering thermoplastics. Paramax® is miscible with polycarbonate andpolysulfone. Paramax® has a high surface hardness which providesexcellent scratch resistance. Other exemplary transparent materialshaving high glass transition temperatures include SUNTUF®, PALSUN® andPALTUF™ polycarbonate sheets, PALGLAS® acrylic sheets; PAL-G™co-polyester sheets, and PALRUF® PVC sheets, all available from Suntuf,Inc. Kutztown, Pa.

According to embodiments of the present invention, transparent acrylicand polycarbonate materials having high glass transition temperaturesare processed with a supermicrocellular foaming technique developed byWright Materials Research Co., Beavercreek, Ohio. This techniqueutilizes biphenyl endcapped poly(acrylene ether) polymers.

Other exemplary transparent materials having high glass transitiontemperatures include Trogamid® brand transparent polyamides (Degussa AG,Marl, Germany). Trogamid® brand transparent polyamides are permanentlytransparent, have high chemical resistance, and have a low tendency tocreep.

Other exemplary materials that can be formed and annealed, in accordancewith embodiments of the present invention, include laminates and/orblends of transparent polymeric materials. Exemplary blends oftransparent polymers include, but are not limited to, polyester blendssuch as polybutylene terephthalate (PBT) blends and polyethyleneterephthalate (PET) blends. Polyester blends, in general, have highstrength and rigidity. Exemplary transparent laminates include, but arenot limited to, polycarbonate-based laminates, acrylic-based laminates,Paramax® brand polymers, polycarbonates, and polysulfone.

Referring to FIG. 3, a method of making a removable dental positioningappliance according to an embodiment of the present invention includesforming a sheet of transparent curable polymeric material into a shellhaving cavities shaped to receive and reposition teeth from a firstorientation to a successive orientation (Block 200) and then curing thepolymeric material (Block 210). When cured, the transparent polymericmaterial preferably has a tensile strength at yield of greater than6,000 psi, preferably has an elongation at yield of greater than 4%,preferably has an elongation at break of greater than 80%, preferablyhas a tensile modulus greater than 200,000 psi, preferably has aflexural modulus greater than 200,000 psi, preferably has stressrelaxation over time of not more than 50%, and preferably has atransmissivity of light between 400 nm and 800 nm greater than 75%. Evenmore preferably, the cured transparent polymeric material preferably hasa tensile strength at yield of greater than 8,800 psi, preferably has anelongation at yield of greater than 5%, preferably has an elongation atbreak of greater than 100%, preferably has a tensile modulus greaterthan 300,000 psi, preferably has a flexural modulus greater than 330,000psi, preferably has stress relaxation over time of not more than 30%,and preferably has a transmissivity of light between 400 nm and 800 nmgreater than 80%.

Exemplary curable transparent polymeric materials that may be utilizedin accordance with embodiments of the present invention include, but arenot limited to, epoxies, sol-gel coatings, polyurethanes, polyureas, andunsaturated polyesters.

According to embodiments of the present invention, curing thetransparent polymeric material may be performed by irradiating thetransparent polymeric material with ionizing electromagnetic radiationsuch as gamma radiation, ultraviolet radiation, microwave radiation,electron beam radiation, x-ray radiation, etc. To facilitate curing withionizing electromagnetic radiation, the transparent polymeric materialmay contain various additives including, but not limited to, radiationstabilizers and antioxidants which act to protect the polymeric materialfrom damage caused by the radiation. Such additives are referred to as“antirads” and function either as reactants, combining readily withradiation-generated free radicals in the polymer material, or as energyabsorbers, preventing the radiation from interacting with the polymeritself.

In addition to curing, ionizing radiation may be utilized to enhance thematerial characteristics of polymers used in dental positioningappliances in accordance with embodiments of the present invention. Manyimportant physical and chemical properties of polymers can be modifiedwith ionizing radiation including, but not limited to, molecular weight,polymer chain length, entanglement, polydispersity, branching, pendantfunctionality, and chain termination. Radiation, such as gamma andelectron beam irradiation, may also be utilized to sterilize thepolymeric material of dental positioning appliances, according toembodiments of the present invention.

Embodiments of the present invention are not limited to curing withionizing electromagnetic radiation. Curing may also be performed via theaddition of heat (i.e., thermal curing), as would be understood by thoseskilled in the art.

Applicants have discovered that removable dental positioning appliancescoated with materials as described above are less susceptible to stressrelaxation and creep than conventional dental positioning appliances.Moreover, Applicants have discovered that removable dental positioningappliances coated with materials as described above are less susceptibleto degradation caused by exposure to saliva and other chemicals in apatient's mouth.

Referring to FIG. 4, a method of making a removable dental positioningappliance according to an embodiment of the present invention includesforming a sheet of transparent curable polymeric material into a shellhaving cavities shaped to receive and reposition teeth from a firstorientation to a successive orientation (Block 300) and then coating thepolymeric shell with a second transparent material (Block 310). If thecoating is a curable material, the shell and coating are then subjectedto curing operations (Block 320) to cure the coating material. Accordingto embodiments of the present invention, curing operations may beperformed by irradiating the transparent polymeric material withionizing electromagnetic radiation such as gamma radiation, ultravioletradiation, microwave radiation, electron beam radiation and x-rayradiation. To facilitate curing with ionizing electromagnetic radiation,the transparent polymeric material may contain various additivesincluding, but not limited to, radiation stabilizers and antioxidants.Embodiments of the present invention are not limited to curing withionizing electromagnetic radiation. Curing may also be performed via theaddition of heat (i.e., thermal curing), as would be understood by thoseskilled in the art.

A coated polymeric shell of a removable dental positioning appliance,according to embodiments of the present invention, preferably has atensile strength at yield of greater than 6,000 psi, preferably has anelongation at yield of greater than 4%, preferably has an elongation atbreak of greater than 80%, preferably has a tensile modulus greater than200,000 psi, preferably has a flexural modulus greater than 200,000 psi,preferably has stress relaxation over time of not more than 50%, andpreferably has a transmissivity of light between 400 nm and 800 nmgreater than 75%. Even more preferably, the coated polymeric shell has atensile strength at yield of greater than 8,800 psi, preferably has anelongation at yield of greater than 5%, preferably has an elongation atbreak of greater than 100%, preferably has a tensile modulus greaterthan 300,000 psi, preferably has a flexural modulus greater than 330,000psi, preferably has stress relaxation over time of not more than 30%,and preferably has a transmissivity of light between 400 nm and 800 nmgreater than 80%.

According to embodiments of the present invention, the first transparentmaterial used to form the shell may include polyurethanes, liquidcrystalline polymeric materials, styrenics, ion-containing polymers,polymeric laminates and polymeric blends. Exemplary liquid crystallinepolymeric materials include, but are not limited to, polyesters,polyamides, polycarbonates, polyolefins, poly(cycloolefins), branchedliquid crystalline polymers and polyarylates.

Exemplary styrenic polymeric materials according to embodiments of thepresent invention include, but are not limited to polystyrene (PS),expanded polystyrene (EPS), acrylonitrile-butadiene-styrene (ABS),styrene-acrylonitrile (SAN), styrene block copolymers (SBC), unsaturatedpolyester resins (uPES), styrene butadiene rubber (SBR), and styrenebutadiene latex (SBL). Exemplary ion-containing polymeric materialsinclude, but are not limited to, Surlyn® brand resin and Nafion® brandpolymers.

According to embodiments of the present invention, the first transparentmaterial used to form the shell may have a glass transition temperatureof at least 100° C.

According to embodiments of the present invention, the first transparentmaterial used to form the shell may include filler material including,but not limited to, inorganic materials and/or organic materials.Exemplary inorganic filler materials include, but are not limited to,metal oxides, oxygenates, carbonates, halides, and sulfates. Exemplaryorganic filler materials include, but are not limited to, waxes andoligomeric polymers.

According to embodiments of the present invention, the first transparentmaterial used to form the shell may include ultra-high molecular weightpolymers.

According to embodiments of the present invention, the first transparentmaterial used to form the shell may include uniaxially oriented polymersand/or bi-axially oriented polymers.

According to embodiments of the present invention, the first transparentmaterial used to form the shell may include Barix® brand vapor barrierfilm.

According to embodiments of the present invention, the secondtransparent material may be a curable polymeric material. Exemplarycurable coating materials, according to embodiments of the presentinvention, include, but are not limited to, epoxies, acrylics, alkyds,acrylate resins which incorporate corrosion protective fillers and othermaterials, multifunctional acrylates (MFMs), acrylated oligomers, ormonofunctional diluent monomers, solvent free powder coatings, sol-gelcoatings, polyurethanes, polyureas, and unsaturated polyesters. Variousphotoinitiators may be utilized including, but not limited to, freeradical, acid, cationic, etc. Curing the second transparent material mayinclude irradiating the coating with ionizing electromagnetic radiation,such as gamma radiation, ultraviolet radiation, microwave radiation,electron beam radiation, x-ray radiation, etc. The second transparentmaterial may include radiation stabilizers and/or antioxidants.

According to embodiments of the present invention, the secondtransparent material may be durable, non-curable polymeric material.Exemplary non-curable polymeric materials include, but are not limitedto, acrylics, silicone, inorganic-containing materials, polycarbonates,and polyurethanes.

According to embodiments of the present invention, the secondtransparent material has a glass transition temperature or a meltingpoint of at least 150° C.

According to embodiments of the present invention, the secondtransparent material includes Barix® brand vapor barrier film.

According to embodiments of the present invention, the secondtransparent material includes advanced thermoplastic composite (ATC)material.

According to embodiments of the present invention, the secondtransparent material includes ISOPLAST® 2530 polyurethane resin (The DowChemical Company, Midland, Mich.). ISOPLAST® 2530 polyurethane resin isa clear amorphous polymer with excellent chemical resistance, high heat,low moisture sensitivity, toughness, and dimensional stability.

According to embodiments of the present invention, the secondtransparent material may contain a material, such as silicon dioxide, toimprove abrasion resistance of the removable dental positioningappliance. According to embodiments of the present invention, the secondtransparent material may contain a material, such as silicon dioxide,that serves as a barrier to harmful substances (e.g., water vapor,oxygen, etc.). According to embodiments of the present invention, thesecond transparent material may contain a material that avoids theformation of fog. Exemplary antifog materials include, but are notlimited to, silicon oxides.

In each of the above-described embodiments, the transparent polymericmaterial of the dental positioning appliance may include uniaxiallyoriented polymers and/or bi-axially oriented polymers.

In each of the above-described embodiments, the transparent polymericmaterial of the dental positioning appliance may include filler materialincluding, but not limited to, inorganic materials and/or organicmaterials. Exemplary inorganic filler materials include, but are notlimited to, metal oxides, oxygenates, carbonates, halides, and sulfates.U.S. Pat. Nos. 5,372,796 and 5,670,583, each of which is incorporatedherein by reference in its entirety, describe metal oxide clusters andceramers (polymer-ceramic composites). According to embodiments of thepresent invention, alloys of polymers with ceramic particles of diametermuch smaller than the wavelength of visible light can be used to producea material with a high refractive index, and that are scratch andcorrosion resistant. Exemplary organic filler materials include, but arenot limited to, waxes and oligomeric polymers.

In each of the above-described embodiments, the transparent polymericmaterial of the dental positioning appliance may include additives, suchas ultra-high molecular weight polymers. An exemplary ultra-highmolecular weight polymer that may be utilized in accordance withembodiments of the present invention is ultra-high molecular weightpolyethylene (UHMWPE), available from Cambridge Polymer Group, Boston,Mass. The wear properties of ultra-high molecular weight polymers, aswell as other types of polymers, can be enhanced with radiation, such aselectron beam and gamma irradiation.

1. A method of making a removable dental positioning appliance,comprising: forming a sheet of transparent polymeric material into ashell having cavities shaped to receive and reposition teeth from afirst orientation to a successive orientation; and annealing the shellat a temperature above a glass transition temperature of the transparentpolymeric material.
 2. The method of claim 1, wherein the transparentpolymeric material comprises amorphous polymeric material and whereinannealing the shell comprises heating the amorphous polymeric materialto a temperature above a glass transition temperature of the amorphouspolymeric material for a period of time sufficient to selectivelydensify the amorphous polymeric material.
 3. The method of claim 1,wherein the transparent polymeric material comprises amorphous polymericmaterial and wherein annealing the shell comprises heating the amorphouspolymeric material to a temperature above a glass transition temperatureof the amorphous polymeric material for a period of time sufficient toselectively crystallize the amorphous polymeric material.
 4. The methodof claim 1, wherein the transparent polymeric material comprisessemi-crystalline polymeric material and wherein annealing the shellcomprises heating the semi-crystalline polymeric material to atemperature above a glass transition temperature of the semi-crystallinepolymeric material for a period of time sufficient to selectivelydecrease stress in the semi-crystalline polymeric material.
 5. Themethod of claim 1, wherein the transparent polymeric material comprisessemi-crystalline polymeric material and wherein annealing the shellcomprises heating the semi-crystalline polymeric material to atemperature above a glass transition temperature of the semi-crystallinepolymeric material for a period of time sufficient to selectivelyenhance crystallization of the semi-crystalline polymeric material. 6.The method of claim 1, wherein the transparent polymeric materialcomprises semi-crystalline polymeric material and wherein annealing theshell comprises heating the semi-crystalline polymeric material to atemperature above a glass transition temperature of the semi-crystallinepolymeric material for a period of time sufficient to selectivelydensify the semi-crystalline polymeric material.
 7. The method of claim1, wherein the transparent polymeric material comprises semi-crystallinepolymeric material and wherein annealing the shell comprises heating thesemi-crystalline polymeric material to a temperature above a glasstransition temperature of the semi-crystalline polymeric material for aperiod of time sufficient to selectively increase or decrease themodulus of the semi-crystalline polymeric material.
 8. The method ofclaim 1, wherein the shell is annealed such that the transparentpolymeric material has a tensile strength at yield of greater than 6,000psi, an elongation at yield of greater than 4%, an elongation at breakof greater than 80%, a tensile modulus greater than 200,000 psi, aflexural modulus greater than 200,000 psi, stress relaxation over timeof not more than 50%, and a transmissivity of light between 400 nm and800 nm greater than 75%.
 9. The method of claim 1, wherein the shell isannealed such that the transparent polymeric material has a tensilestrength at yield of greater than 8,800 psi, an elongation at yield ofgreater than 5%, an elongation at break of greater than 100%, a tensilemodulus greater than 300,000 psi, a flexural modulus greater than330,000 psi, stress relaxation over time of not more than 30%, and atransmissivity of light between 400 nm and 800 nm greater than 80%. 10.The method of claim 1, wherein annealing is performed at a temperaturebetween the glass transition temperature of the transparent polymericmaterial and the melting temperature of the transparent polymericmaterial.
 11. The method of claim 1, wherein annealing is performed forat least about one minute.
 12. The method of claim 1, wherein thetransparent polymeric material is selected from the group consisting ofliquid crystalline polymeric materials, styrenics, and ion-containingpolymers.
 13. The method of claim 1, wherein the transparent polymericmaterial comprises filler material selected from the group consisting ofinorganic materials and organic materials.
 14. The method of claim 1,wherein the transparent polymeric material comprises inorganic fillermaterial selected from the group consisting of metal oxides, oxygenates,carbonates, halides, and sulfates.
 15. The method of claim 1, whereinthe transparent polymeric material comprises organic filler materialselected from the group consisting of waxes and oligomeric polymers. 16.The method of claim 1, wherein the transparent polymeric materialcomprises ultra-high molecular weight polymers.
 17. The method of claim1, wherein the transparent polymeric material comprises liquidcrystalline polymeric material selected from the group consisting ofbranched liquid crystalline polymers and polyarylates.
 18. The method ofclaim 1, wherein the transparent polymeric material comprises styrenicpolymeric material selected from the group consisting ofacrylonitrile-butadiene-styrene (ABS), styrene-acrylonitrile (SAN), andstyrene block copolymers (SBC).
 19. The method of claim 1, wherein thetransparent polymeric material comprises Surlyn® brand resin.
 20. Themethod of claim 1, wherein annealing is performed only on a selectedportion of the shell.
 21. A method of making a removable dentalpositioning appliance, comprising: forming a sheet of transparentcurable polymeric material into a shell having cavities shaped toreceive and reposition teeth from a first orientation to a successiveorientation; and curing the transparent polymeric material, wherein thecured polymeric material has a tensile strength at yield of greater than6,000 psi, an elongation at yield of greater than 4%, an elongation atbreak of greater than 80%, a tensile modulus greater than 200,000 psi, aflexural modulus greater than 200,000 psi, stress relaxation over timeof not more than 50%, and a transmissivity of light between 400 nm and800 nm greater than 75%.
 22. The method of claim 21, wherein thetransparent curable polymeric material is selected from the groupconsisting of epoxies, acrylics, alkyds, acrylate resins whichincorporate corrosion protective fillers and other materials,multifunctional acrylates (MFMs), acrylated oligomers, monofunctionaldiluent monomers, solvent free powder coatings, sol-gel coatings,polyurethanes, polyureas, and unsaturated polyesters.
 23. The method ofclaim 21, wherein curing the transparent polymeric material comprisesirradiating the transparent polymeric material with ionizingelectromagnetic radiation selected from the group consisting of gammaradiation, ultraviolet radiation, microwave radiation, electron beamradiation and x-ray radiation.
 24. The method of claim 23, wherein thetransparent curable polymeric material comprises radiation stabilizers.25. The method of claim 23, wherein the transparent curable polymericmaterial comprises antioxidants.
 26. A method of making a removabledental positioning appliance, comprising: forming a sheet of transparentcurable polymeric material into a shell having cavities shaped toreceive and reposition teeth from a first orientation to a successiveorientation; and curing the transparent polymeric material, wherein thecured polymeric material has a tensile strength at yield of greater than8,800 psi, an elongation at yield of greater than 5%, an elongation atbreak of greater than 100%, a tensile modulus greater than 300,000 psi,a flexural modulus greater than 330,000 psi, stress relaxation over timeof not more than 30%, and a transmissivity of light between 400 nm and800 nm greater than 80%.
 27. The method of claim 26, wherein thetransparent curable polymeric material is selected from the groupconsisting of epoxies, acrylics, alkyds, acrylate resins whichincorporate corrosion protective fillers and other materials,multifunctional acrylates (MFMs), acrylated oligomers, or monofunctionaldiluent monomers, solvent free powder coatings, sol-gel coatings,polyurethanes, polyureas, and unsaturated polyesters.
 28. The method ofclaim 26, wherein curing the transparent polymeric material comprisesirradiating the transparent polymeric material with ionizingelectromagnetic radiation selected from the group consisting of gammaradiation, ultraviolet radiation, microwave radiation, electron beamradiation and x-ray radiation.
 29. The method of claim 28, wherein thetransparent curable polymeric material comprises radiation stabilizers.30. The method of claim 28, wherein the transparent curable polymericmaterial comprises antioxidants. 31-54. (canceled)